Amyotrophic lateral sclerosis 2 (ALS2) is an autosomal recessive form of juvenile onset ALS characterized by spasticity of limb and facial muscles resulting from degeneration of motor neurons in the central nervous system. A gene responsible for ALS2 disease has recently been cloned that encodes a protein (termed alsin) with domains suggestive of functions in cell signaling, intracellular trafficking, and cytoskeletal organization. To gain further insight into the normal biological function of this gene, we propose to create a model of this disorder in the fruit fly Drosophila melanogaster. The Drosophila ALS2 gene (DALS2) encodes a polypeptide with 23% amino acid identity (38% similarity) to the human alsin polypeptide and is broadly expressed in a variety of tissue types throughout development. We propose to generate mutations in DALS2 using gene-targeting and double stranded RNA interference methods. Resulting DALS2 mutants will be characterized for signs of progressive motor neuron dysfunction and defects in cell signaling, intracellular trafficking, and cytoskeletal assembly. Additionally, we will conduct screens for genetic modifiers of the DALS2 phenotypes to elucidate the biochemical pathways leading to neuronal dysfunction and death in this Drosophila ALS2 disease model. Results from this work should clarify the normal cellular role of the ALS2 gene and may reveal strategies for treatment of ALS disease.